package 网易机试;

import java.util.Arrays;
import java.util.Scanner;

public class 第二题 {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        while (sc.hasNext()) {
            int n = sc.nextInt();
            int[] a = new int[n];
            for (int i = 0; i < n; i++) {
                a[i] = sc.nextInt();
            }
            System.out.println(f(a));
        }
        sc.close();
    }

    private static String f(int[] a) {
        Arrays.sort(a);
        int d = a[1] - a[0];
        for (int i = 1; i < a.length; i++) {
            if (a[i] - a[i - 1] != d)
                return "Impossible";
        }
        return "Possible";
    }
}
